Offshore gas field development
The Crux project involves the development of the Crux gas field located in Browse Basin, approximately 160km offshore north-west Australia.
The gas field is being developed by a joint venture comprised of Shell Australia, a subsidiary of Royal Dutch Shell (82%, operator), SGH Energy, a subsidiary of Seven Group Holdings (15%), and Osaka Gas Holding (3%). It will supply backfill gas to the Prelude floating liquefied natural gas (FLNG) facility, which is the world’s biggest FLNG platform.
Currently, the Crux project is pending government approval, following which the final investment decision is expected to be made in 2020. The front-end engineering design (FEED) studies for the project have commenced and foundation development drilling for the project is expected to start in 2021.
Following an expected life of 20 years, the field will be abandoned and decommissioned. It is estimated to have a production capacity of 2.9 million tonnes per annum (Mtpa).
The Crux gas field is located in the AC/P23 permit in the Commonwealth marine waters of the Browse Basin in water depths from 110m to 170m.
Discovered in 2000, the Crux gas field was initially operated by Nexus, which is now part of SGH.
The field consists of four reservoir units of the Montara, Plover and Nome formation. It is estimated to contain two trillion cubic feet of gas and 66 million barrels of condensate.
The Crux gas field is planned to be developed through a not normally manned (NNM) platform equipped with dry trees, minimal processing facilities and utility systems. The NNM platform will be remotely operated from the Prelude FLNG facility.
Five production wells are planned to be drilled from a single drill centre. The wells will be tied-back to the platform through subsea infrastructure. Additional wells are planned to be drilled within the Crux in-field development area, approximately 30km from the proposed platform location. The additional wells will also be tied-back to the platform using subsea infrastructure.
The NNM platform will be tied-back to the Prelude FLNG facility through a subsea tie-in system and a 165km-long and 26in diameter export pipeline. The proposed route of the export pipeline does not have any seabed obstructions and is relatively straight. It will include a 1km buffer on both sides to accommodate for minor deviations in the final pipeline route.
Prelude FLNG facility is installed in a water depth of 250m in the Browse Basin as part of the Prelude field development plan. It has a production capacity of 5.3Mtpa of liquids, 3.6Mtpa of LNG, 1.3Mtpa of condensate and 0.4Mtpa of liquefied petroleum gas.
The 488m-long vessel weighs 600,000t and is secured in position by a 93m-high turret mooring system. It commenced production in December 2018 and is set to enter start-up and ramp-up phase.
Designed to withstand Category 5 cyclones, the facility enables natural gas produced offshore to be liquefied and offloaded onto ocean-going LNG carriers for transportation to customers.
Wood and KBR were awarded the contract for delivering the FEED for the NNM platform and gas export pipeline of the Crux project.
Neptune was contracted to perform geotechnical surveys for the field as well as route survey for the 160km pipeline. The company used its Mermaid Investigator offshore supply vessel to carry out the studies.
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